1. Field of the invention
This invention relates to a battery. More particularly, it relates to an active substance for an electrode in which alkali metals such as lithium, potassium, etc., alkaline earth metals, rare earth metals, or transition metals are used as a dopant, or halogens, halogen compounds, or oxygen acids are used as a dopant. It also relates to a secondary battery with a nonaqueous electrolytic solution, which comprises a negative electrode made of carbon materials that can reversibly absorb or release light-weight metals such as lithium, potassium, etc.
2. Description of the prior art
Secondary batteries that use lithium or other such alkali metals have received more attention as the miniaturization and energy-saving changes in electronic machinery, etc., have proceeded, and these batteries are now at the stage in which they can be used in practice. As the negative electrode, light-weight metals such as lithium, potassium, or light-weight metal alloys such as an alloy of lithium and aluminium or Wood's metal as representative low-melting-point alloys are used; for the positive electrode on the other side, metal oxides such as vanadium pentaoxide, chromiun trioxide, etc., chalcogen compounds such as titanium disulfide, organic polymers, or the like are mainly used.
It has been tried to use carbon materials in the electrodes of batteries. For example, active carbon or active carbon fiber has been used as the electrode materials, but the lamination layer of the hexagonal net faces that are constituted by the carbon atoms is not completely regular, so it is not possible to dope the carbon with each ion, and only electric double layer can be formed at the interface between the carbon and the electrolyte. Therefore, when these substances are used as the materials for the negative electrode, it is difficult to bring about doping with positive ions, and it is not possible to obtain more than the electric capacity that corresponds to the amount of ions to be accumulated into the electric double layer. The structure with a regular arrangement of hexagonal net faces made of carbon atoms is called a graphite structure. It has a laminated structure in which the carbon layers with the hexagonal net faces have stacked regularly with each other. It is possible for the dopant to have access to the spaces between the layers, but the space is narrow, 3.354 .ANG., and moreover, the hexagonal net faces have accumulated in a very regular manner, so that only a small quantity of dopant will be involved in doping at temperatures near room temperature. There is also a carbon material with a structure that is intermediate between amorphous carbon (like the above-mentioned activated carbon), the layered structure of which is completely irregular, and graphite, the layered structure of which is completely regular. This intermediate structure is generally called a turbostaratic structure, and many carbon materials in this category are known.